Currently used telecommunications networks are a combination of logically separated networks, comprising the public telephone network to carry voice and voice-band data and a variety of special services networks to carry various services such as corporate wide area networks or the Internet traffic. With the availability of very high speed fiber-optic links and techniques such as Asynchronous Transfer Mode (ATM), there is a migration towards integrating all of these networks into one Broadband ISDN network that is truly multi-class as well as multi-rate. A driving force for this integration is the ease of administering and maintaining the network. However, an integrated network must be considered in view of the current state of the art. Restoral around link failures is a particular area of concern. Presently, there is no attempt to restore a voice call around a failure; one simply is expected to re-dial. In the next-generation network, if a failure occurs during a multi-hour video call and the receiver is amenable to concealing small glitches, then the call could be restored as quickly as possible. Vital information (such as financial news feeds) was traditionally carried over special networks that were completely duplicated to minimize losses. Even this method fails if an entire central office is taken out of service.
If the traffic is to carried on a B-ISDN network, a very fast recovery from failures is essential. Another aspect of the next-generation network is the volume of information being transmitted on a single link where a single break can remove a large cross-section of the users from the network and a quick restoral is essential if the operating company is to maintain its reputation as a reliable service provider.
In present networks, restoral is a slow, time-consuming process done by a centralized restoral system. The control information for restoral is carried on a separate X.25 network to a centralized controller. If a link failure is noticed, information about the failure is first sent to the centralized controller. Then, the central controller runs an algorithm to restore the trunks on the failed link. This process typically is used for special services where the intent is not to restore lost data but rather to restore lost services as soon as possible. Restoral times on the order of a few hours is not unrealistic currently. However, a new approach, to restore traffic on a call-by-call basis, is necessary. This is the principal focus of the present invention, in which the problem of fault tolerance of high-speed networks is considered and a solution is provided where a distributed link-based alternative routing scheme guarantees that the network will survive under any single link failure. A principal object of the solution is to achieve network survival with very little restoral delay.